Bark-removing apparatus having barkimpacting hammers



July 30, 1957 w. A. HOSMER BARK-REMOVING APPARATUS HAVING BARK-IMPACTINGHAMMERS 2 Sheets-Sheet l July 30, 1957 w. A. HOSMER BARK-REMOVINGAPPARATUS HAVING BARK-IMPACTING HAMMERS Filed m 5, 1952 2 Sheets-Sheet 2BARK-REMOVWG APPARATUS HAVING BARK- IMPACTHNG HAMMERS Windsor ArnoldHosmer, Belmont, Mass.

Application Aagust 5, 1952, Serial No. 392,773

16 Claims. (Cl. 144-208) This invention pertains to apparatus forseparating the bark from parts of trees, for example, pulp logs orbolts, as a preliminary step in the preparation of paper pulp orsaw-logs preparatory to sawing. It may also be used to remove bark fromslabs or edgings produced in a sawmill from unbarked logs. Variousmechanical and hydraulic mechanisms have heretofore been proposed andused for removing the bark from logs, but none of these prior deviceshas proven entirely satisfactory so that hand-peeling of the bark isstill used under some circumstances.

The bark of a log is firmly attached to the wood at the cambium layer;the logs to be de-barked are of different diameters and a given log mayvary substantially in diameter from end to end; the logs are notmathematically straight or cylindrical and often have knots and otherprojections, and the bark may vary greatly in thickness on differentlogs, or even on the same log.

In order that it may be practical and acceptable to the industry, adebarking apparatus should remove a very large percentage of the barkregardless of irregularities in the log, so that hand peeling is reducedto a minimum. On the other hand, such apparatus should be so designed asto avoid substantial chipping of the wood.

The present invention has for its principal object the provision ofapparatus for use in separating the bark from the log, and in particularso to separate the bark as to leave the log substantially clean and bareand without chipping into the log, and in such a way that relativelysmall power is required and by a procedure and means applicable to logsof the usual sizes and having the irregularities customarily encounteredin pulp or saw log operations. Specifically, the force for loosening thebark, in accordance with the present invention, is applied as a wedgeaction, a wedge element, having its apex edge extending lengthwise ofthe log, being forced through the bark and exerting loosening forcesimultaneously in opposite directions circumferentially away from aplane which contain the wedge apex and the longitudinal axis of the log,or a line parallel to said axis. By progressing this wedge action fromend to end of the log, and by applying such wedge action at a sufficientnumber of spaced, longitudinally extending planes, the entire sheath ofbark is loosened and separated from the wood. A desirable feature in thepractice of the invention is the cutting of the bark circumferentiallyof the log at spaced intervals lengthwise of the log, preferablysimultaneously with the application of the wedging force, therebyseparating the bark into relatively small pieces which are readilyconveyed away from the bark-loosening apparatus.

The present invention is based upon the discovery that if force beapplied to the bark in longitudinally extending planes, by wedge-shapedimplements which cut or impress longitudinally extending grooves orchannels into the bark, thereby creating components of force which actsubstantially tangent to the surface of the wood in in Q6 ice oppositedirections at the cambium layer, such force cracks and loosens the barkfrom the harder wood at the cambium layer. When force is thus applied bya barkpenetrating wedge, the resistance of the bark (being less thanthat of the wood) causes the bark to be loosened even at irregularportions of the log, and with only a slight indentation of the wood andwithout substantial chipping. While good results are obtained by the useof wedges which form longitudinal grooves only, optimum results aresecured by forming additional grooves by wedges whose apex edges extendtransversely of the log. The bark is thus cut into pieces of shortlength while at the same time these transversely extending wedges exerta component of force in a direction lengthwise of the log which furtherassists in cracking the bark from the wood at the cambium layer. Thusthe log is left substantially bare of bark, so that little, if any,manual labor is required in cleaning the log for the pulping operation.

Further objects and advantages of the invention will be pointed out ingreater detail and by reference to the accompanying drawings wherein:

Fig. 1 is a transverse section through a log, illustrating the principleof loosening the bark in accordance with the present invention;

Fig. la is a fragmentary diagrammatic transverse section, to largescale, illustrating the forces which are believed to be efiective inloosening the bark.

Fig. 2 is a perspective view of a log, illustrative of the type ofincisions formed in the bark according to the present invention butwithout attempt to show the actual number of incisions which is formed;

Fig. 3 is a diagrammatic side elevation of apparatus useful in thepractice of the method of the invention;

Fig. 4 is a diagrammatic end elevation showing means for advancing thelog for the de-barking operation;

Fig. 5 is an end elevation, diagrammatic in character, illustrating adesirable arrangement of rotors about the circumference of the log;

Fig. 6 is a side elevation, to larger scale, illustrating one of therotors which carries the Wedge elements for loosening the bark;

Fig. 7 is a fragmentary end elevation of the rotor, partly in section,as indicated by the line 77 in Fig. 6;

Fig. 8 is a fragmentary, perspective view of a combined wedge elementand cutter;

Fig. 9 is a section on line 99 of Fig. 7;

Fig. 10 is a diagrammatic elevation illustrative of a desirable way ofsupporting and driving one of the rotors; and

Fig. 11 is a fragmentary perspective view showing a modification.

Referring to Figs. 1, la and 2, the numeral 1 indicates a bolt of woodor a log such as is used in the pulp or sawmill industry, such log beingof any length and diameter customary in those industries. This logcomprises the core 2 of solid wood, and the bark 4 which adheres veryfirmly to the wood at the cambium layer 3. In accordance with thepresent invention, the bark is loosened from the wood at the cambiumlayer by forcing a wedge element 5 through the bark so as to formlongitudinally extending incisions S. The wedge element hereinillustrated has beveled or inclined faces at opposite sides whichconverge toward the edge, the latter lying in a medium plane of thewedge element, said median plane bisecting the angle between the edgefaces so that the wedge action, when the wedge element is forced intothe bark, is substantially equal in opposite directions. The inwardmovement of this wedge element creates force having components in thedirection of the arrows F and F tangential to the log and in oppositedirections, acting upon the t bark" at the opposite sides of theincision formed by the inward moving" wedge, this" wedge having acutting or apex edge which is longitudinal of the log. The resultofrthis crowding of the bark in opposite directions is to cause the,bark at opposite sides" of the wedge to crack away from the'wood at atangential plane with there'- sult that the bark is loosened from thewood. By introducing such wedge elements at intervals sufiiciently closecircumferentially of the log, the entire sheet of bark may be loosenedat the cambium layer in the form of longitudinally extendingstrips, itbeing understood that the log and wedge elements will be relativelymoved so that the incisions -S, formed by the wedge elements, willextend substantially continuously from end to end of the log.Preferably, to facilitate the removal ofthese loose strips,.circurnferentially extending incision 10 (Fig; 2) will be formed suchas to connect the longitudinal incisions S formed by the wedge elements.As a result of this operation, the bark separates from the wood at thec'ambium layer innarrow strips of relatively short length, such as. mayreadily be conveyed away by appropriate conveyor means, leaving the logsubstantially bare and requiring butlittle further cleaning to prepareit for the chipping or sawing operation.

The introduction of the wedge elements may be carried out as a handoperation, the wedge elements being forced through the bark, forexample, by striking the Wedge elements with a mallet, but forcommercial purposes it is desirable to employ power-driven apparatus forforcing the wedge elements through the bark. Figs. 3 to 5 anddiagrammatically illustrate appropriate apparatus which is generallyindicated by the numeral 11 (Fig. 3). This apparatus comprises. suitablemeans for advancing the log in an axial direction while the bark isbeing loosened. As here illustrated, this means comprises a series ofrolls 12 on which the log rests, these rolls preferably being in pairs,for instance, as illustrated in Fig. 4, the rolls of each pair beingspaced axially and secured to a shaft 13 supported in suitable bearings(not illustrated) in the machine frame. Each of these shafts 13 isprovided, for example, with a sprocket wheel 14 which receives apower-driven chain, so as to turn the rolls 12 at the desired speed.These log advancing, rolls may be of any desired construction which isetfectiveto advance the log. Desirably these rolls should have teeth,ribs, spikes or other means for obtaining a very firm grip onthe log,and for this purpose might, for example, consist merely of a series ofradiating, sharppointed arms carried by the shaft 13 so devised that thelog will rest upon the points of these arms. The particular type of rollforms no essential part of the invention provided, as above described,it grips'the log positively enough to insure theforward propulsion ofthe log. h

At spaced intervals along the length of'the log pairs of shafts 15, 16,etc. are arranged on which are mounted the carriers for the wedgeelements. As suggested in Fig. 5, there are four pairs of these shafts,but the number may be increasedor decreased depending on the range ofsizes of logs for which a particular machine is designed. The

axes of all of these shaftsare in planes perpendicular to thelongitudinal axis of the log. Preferably the shafts of each respectivepair (for example, the shafts 15 and 16) are diametrically opposite, asrespects the axis of the log, and, preferably, the axes of the severalsuccessive pairs lie in planes parallel to the log axis and definingside faces of'a regular prism. If four pairs are used (Fig. 5) theseplanes would form an octagonal prism. The shafts of each pair areparallel to a tangent to the circumferential surface of the log, but areat such distances from the axis of the log as to provide for the propermotion of the wedge carrying elements. I

7 To permit the rotor to follow irregularities in the log, the rotor ismounted to permit it to move bodily toward or from'the axis of the log.For example, as illustrated in Fig. 10, the shaft 15 of the rotor R maybe mounted in bearings at one end of a tiltable frame T, fulcrumed athaving a simple wedgeyele'ment at its end, itis desirable, as I Aso asto swing about an axis in a plane perpendicular to the axis of the logand parallel'to a tangent to the surface of the log. Each rotor may bedriven by an independent motor M, shown in Fig. 10 as mounted on thecorresponding frame T at the opposite side of the fulcrum from therotor, and driving the rotor by means of a belt B. However, any otherappropriate drive means may be employed.

The parts are so designed that the rotor tends to approach the axis ofthe log, either by gravity action or by the action of a spring S, orboth, so that the rapidly revolving wedge elements engage the bark withthe desired bark-cracking force but can retreat from the axis of the logwhen they encounter abrupt projections such as knots or in response toan increase in the diameter of the log.

Referring to Figs. 6 and 7, each of these shafts, for example the shaft15, is provided at a point between its ends with a rotor R, shown inFig. 6, as comprising axially spaced headers H and H Two series ofcontiguous crank plates 13, 14 are arranged between the headers, the Icrank members of one series lying out of phase with those of theotherseries. As here shown (Fig. 7), these crank plates are ofelliptical contour though this is not essential. They are fixed to theshaft in any suitable way, as by splining, and have aligned openings forthe passage of the crank pins 17, 18, 19 and 20. Successive crank pinsare spaced 90 circumferentially of the shaft, and each crank pin carriesa series of radial, pivoted arms 21, 22,21 22 etc. free end with a wedgeelement 23 (Fig. 9) having an apex or cutting edge 24 which extendslongitudinally of the log. As here illustrated, each of the arms 21, 22,etc. consists of a length of steel, for example, of the order of inch inthickness and of a width of approximately 1 inch.

A desirable length for the arms 21, 22, etc. is approximate.

ly 4 inches. As shown in Fig. 7, the effective or forward edge of eacharm is beveled for a portion of its length, as indicated at 23 (Fig. 7to provide a wedge-like barkcracking element. An apex angle ofapproximately 30 is cited by way of example as providing good results.Desirably, the free end portion of each arm is curved, as shown at 25,so that this portion of the. arm, which first contacts the bark,presents a curved apex edge which extends longitudinally of the log.

As illustrated in Fig. 5, there are eight'of the rotors R, the axes ofthe several rotors being in planes perpendicular to the axis of the log,and also in planes which define the side faces of a regular octagonalprism. Thus the planes of rotation of the arms of the successive rotors,which are parallel to said axis, intersect at at 45.

While desirable results may be obtained if all of the arms carried byeach of the shafts is of the above type, each above suggested, to formcircumferential incisions 10 at short intervals. For this purpose,certain of the arms 21,,

22, etc. (for instance the arm 21, Fig. 11),. instead of the wedgeelements 23, may carry cutter blades, 27*, generally similar to thewedge elements 23, but extending circumferentially of the log so as toform said circumferential incisions 10 (Pig. 2), thereby to cut the barkinto I relatively short sections. When the rotor turns inrthe directionof the arrow A in Fig. 11 the cutter blades not only cut the bark intoshort lengths, but they also exert a wedge action, similar to that ofthe wedge elements 23, thus assisting in cracking the bark away from thewood. Alternatively, as indicated in Fig. 8, some of the arms, forexample the arm 21 may carry composite cutters, including Wedgeelements, having the apex edges 24 and also transverse members 26 havingcutting edges 27, at right angles to the apex edges 24. These combinedcutter devices may be substituted for so many of the simple wedgeelements as may be found desirable to divide the Each of these arms isprovided at its arrow A (Fig. 7), thereby causing the arms to swingoutwardly centrifugally and thus to acquire a substantial momentum suchthat when they contact the bark, as the log is progressed, the wedgeelements will impact the bark with sufilcient force to pass through thethickness of the bark and thus, as above described with respect to Fig.l, to crack the bark at the cambium layer.

The momentum of the swinging arm is such that the wedge passes throughthe entire thickness of the bark, but, preferably, the wedge should notcut deeply into the solid wood. However, even though the edge doesindent the wood, no harm is done except loss of power, since the wood isnot chipped nor removed. At the lower part of Fig. 7 the positions ofseveral of the arms 22 are illustrated as their edges contact the barkat various points in its circumference. Since the arms swing freely, theonly force available for cutting the bark is that provided by themomentum of the individual arms, and thus the danger of breakage of anyof the parts due to variation in diameter of the log or the presence ofknots or other projections is minimized. With the arrangement disclosed,the wedge elements contact the bark at suitable intervals throughout itsentire circumference so as to split the bark into longi- I tudinalribbons, each of which is thoroughly loosened from the cambium layer. Arotational speed of the shafts of 1800 R. P. M. has been found desirablein attaining the results, but various speeds may be used, depending uponthe character and condition of the logs.

No attempt has been made herein to illustrate in detail the elements ofthe machine frame, since it is obvious that it is within the skill ofthe ordinary mechanic to erect a proper frame structure to support thebearings for the various shafts. It is to be understood that while onedesirable form of apparatus for wedglng the bark away from the cambiumlayer has here been illustrated by way of example, the invention isbroadly inclusive of any and all means whereby the wedge elements may beeifectively forced through the bark in carrying out the aboveprinciples.

From the foregoing it will be evident that the projecting ends of theelliptical plates 13 and 14 provide recesses therebetween for thepivoted ends of the hammers so that the pivot pins for the hammers aresupported on each side of each hammer immediately adjacent the hammer.In. the illustration these recesses are disposed in four rows spaced 90around the periphery of the rotor, the recesses of each row beingstaggered with respect to the recesses of the next preceding andsucceeding rows. Thus the recesses are disposed between planesperpendicular to the axis of the rotor with at least one recess betweeneach pair of adjacent planes, the width of the recesses beingsubstantially equal to the distance between planes and the width of thehammers being substantially equal to that of the recesses, so that thehammers strike the pieces throughout substantially the entire length ofthe rotor and the pivoted end of each hammer may be as wide as itsprojecting portion.

I claim:

1. Apparatus for use in debarking a slab or a log, said apparatuscomprising means for axially and nonrotatably feeding a slab or a log, aplurality of wedge elements each having an apex edge lying in a medianplane of the wedge element which is substantially parallel to the axisof a slab or a log being debarked, and means operative to force each ofsaid wedge elements into the bark as a slab or a log advances axiallyrelatively to said wedge elements whereby the bark is crowded apart inopposite directions tangentially of such a slab or log by each wedgeelement, the se eral wedge elements being transversely spaced so that inapproaching the bark their apex edges strike the bark glancing blowsdirected lengthwise of such a slab or log at circumferentially spacedpoints.

2. Apparatus for use in debarking a log, said apparatus comprising meansfor positioning a log, a plurality of groups of wedge elements, eachwedge element having an elongate apex edge which moves in a planesubstantially parallel to the longitudinal axis of a log being debarked,the wedge elements of each respective group having relative movement inparallel paths, the planes of movement of the elements of one groupintersecting the planes of movement of the elements of the next adjacentgroup, the planes of movement of certain elements of each groupcontaining or extending close to said longitudinal axis, and means forimpacting each wedge element against the bark with force sutlicient tocrack the bark and to crowd the bark in opposite directionscircumferentially of such a log.

3. Apparatus for use in debarking a log, said apparatus comprising meansfor positioning a log, a plurality of groups of wedge elements, eachwedge element having an elongate apex edge which moves in a planesubstantially parallel to the longitudinal axis of a log being debarked,the wedge elements of each respective group having relative movement inparallel paths, the planes of movement of the elements of one groupintersecting the planes of movement of the elements of the next adjacentgroup at an angle of approximately 45, and means for causing each wedgeelement to impact the bark with force sufiicient to crack the barklongitudinally.

4. Apparatus for use in debarking a log, said apparatus comprising meansfor positioning a log, a plurality of groups of wedge elements, eachWedge element having an elongate apex edge which moves in a planesubstantially parallel to the longitudinal axis of a log being debarked,the wedge elements of each respective group having relative movement inparallel paths, the planes of movement of the elements of one groupintersecting the planes of movement of the elements of the next adjacentgroup at an angle of approximately 45, the elements of those groupswhich are disposed at diametrically opposite sides of a log having thesame planes of movement, each pair of oppositely disposed groups ofelements being spaced lengthwise of such a log from an adjacent pair,and means for causing each wedge element to impact the bark of the logwith a force sutficient to crack the bark longitudinally.

5. Apparatus for use in debarking a slab or log, said apparatuscomprising means for positioning such a slab or log, a rotor turningabout an axis which lies in a plane perpendicular to the longitudinalaxis of a slab or log and said rotor axis extending parallel to atangent to such slab or log, an arm carried by the rotor, a wedgeelement carried by the arm, the wedge element having an apex edge lyingin a median plane of the wedge element which is substantially parallelto said longitudinal axis, and means for turning the rotor, the lengthof the arm being such that as the rotor turns the wedge element impactsthe bark by a glancing blow directed lengthwise of such a log.

6. Apparatus for use in debarking a slab or log, said apparatuscomprising means for positioning such a slab or log, a rotor turningabout an axis which lies in a plane perpendicular to the longitudinalaxis of a slab or log being debarked and which lies parallel to atangent to such a slab or log, an arm pivotally connected at one end tothe rotor, a wedge element carried by the arm, the wedge element havingan apex edge which moves in a plane substantially parallel to saidlongitudinal axis, means for turning the rotor, thereby to impact thewedge element against the bark, and means supporting the rotor forbodily movement toward and from said tangent.

7. In apparatus for debarking slabs or logs, in combination, means formoving a slab or log in its axial direction, a rotary shaft whose axisof rotation lies in a plane perpendicular to said axial direction andlies parallel to but spaced from a tangent to such a slab or log beingdebarked, a rotor mounted on the shaft, arms pivoted to the rotor atdiametrically opposite sides of the shaft and at points spaced from theaxis of the shaft, 2.

wedge. element: at the free end of each'arm which moves, in aplanarpath. substantially parallel to said axial direction, saidzwedge elementhaving an apex edge lying in a median plane of the wedge element whichbisects the angle between two convergent faces, and the arms being ofsuch length that as the shaft turns and such a slab or log advances, thewedge elements impact the bark on the slab or log by glancing blowsdirected lengthwise of such slab or log.

1 8. 'In'apparatus' for debarking slabs or logs, in combination, meansfor moving a slab or a log in its axial direction, a rotary shaft whose.axis of rotation lies in a plane perpendicular to said axial directionand lies parallel to but spaced from a tangent to such a slab or logbeing debarked, a rotor mounted on the shaft, the rotor comprisingelongate crank pins parallel to the axis of the shaft and atdiametrically opposite sides of the latter, a plurality of armspivotally connected to each crank pin, a Wedge element at the free endof each arm, each wedge element having an apex edge which moves in aplane substantially parallel to said axial direction, an arm on one ofsaid crank pins containing a plane of movement intervening between theplanes of movement of adjacent arms on the opposite pin, and means forrotating the shaft.

9. In apparatus for debarking slabs or logs, in combination, means formoving a slab or log in its axial direction, a rotary shaft whose axisof rotation lies in a plane perpendicular to said axial direction andlies parallel to but spaced from a tangent to such a slab or log beingdebarked, a rotor mounted on the shaft, the rotor having,

elongate crank pins arranged 90 apart about the axis of the shaft, eachcrank pin being parallel tothe axis of the shaft, a plurality of armseach pivoted at one end on its respective crank pin, certain of saidarms each having a wedge element at its free end, each wedge elementhaving an apex edge movable in a plane parallel to said axial direction,each of certain other arms having a cutter provided with a cutting edgeextending transversely to said axial direction, the arms being of suchlength that as the shaft rotates the wedge elements and cutters impactthe bark, and means for rotating the shaft.

10. In apparatus for debarking logs, in combination, means for advancinga log in its axial direction, rotary shafts whose axes of rotation arein planes perpendicular to and which are spaced longitudinally ofsaidaxial direction, each shaft being parallel to but spaced from a tangentto a log being debarked, the axes of the several shafts lying in planeswhich constituteside faces of a regular prism coaxial with such a log,each shaft carrying a crank pin, an arm pivoted to each crank pin,-certain of said arms carrying wedge elements each having an apex edgewhich moves in a plane parallel to said axial 7 direction, and means forrotating the shaft, thereby to impact the wedge elements against thebark,

11. In apparatus for debarking logs, in combination, means for advancinga log in its axial direction, rotary shafts whose axes of rotation arein planes perpendicular to and which are spaced longitudinally of saidaxial direction, each shaft being parallel to but'spaced froma tangentto a log being debarked, the axes of the several shafts lying in planeswhich constituteside faces of a regular prism coaxial with such a log,each shaft carrying a crank pin, an arm pivoted to each crank pin,certain of said arms carrying wedge elements having apex edges disposedparallel to the axes of the shafts which carry the respective crank pinsand other of said arms carrying wedge elements having apex edges movablein planes parallel to said axial direction, and means for rotating theshaft. 1

12.'In apparatus for debarking logs in combination, means for advancinga log in its axial direction, rotary shafts whose axes of rotation arein planes perpendicular to and spaced longitudinally of said axialdirection, each shaft being parallel to but spaced from a tangent tosuch a log being debarked, the axes of the several shafts lying in p anehich qo t es d f ce o e u rp i m ax al h. u h a oa ac h ft y n a cra k;pin

an arm pivoted to each crank pin, certain of said arrns carryingcombined wedge elements and cutters opezrative.

simultaneouslyto form lengthwise and circumferential incisions in thebark, and means for rotating the several shafts simultaneously.

13; Apparatus for use in debarking a piece: of wood whose bark-coveredsurface is curved transversely and extends relatively straightlongitudinally, said apparatus comprising means for positioning such apiece, a rotor turning about an axis which lies in a plane perpendicularto the-lengthwise axis of a piece being debarked and is parallel to atangent to said curved bark-covered surface, an arm pivotally connectedat one end to the rotor, at the free end of each arm a wedge elementhaving an apex edge which moves in a plane substantially parallel to thelengthwise axis of such a piece, means for turning the rotor to impactthe wedge element against the bark,

and means supporting the rotor for bodily movement toward and from saidtangent.

14. In apparatus for debarking a piece of wood whose bark-coveredsurface is curved transversely and extends relatively straightlongitudinally, in combination, means for moving such a piece in itslengthwise direction, a rotary shaft whose axis of rotation lies in aplane perpendicular to said lengthwise direction and lies parallel tobut spaced from a tangent to said curved bark-covered surface, a rotormounted on the shaft, the rotor comprising elongate crank pins parallelto the axis of the shaft and at diametrically opposite sides of thelatter, a plurality of arms pivotally connected to each crank pin, awedge element at the free end ofeach arm, each wedge element having anapex edge which moves in a plane substantially parallel to saidlengthwise direction, an arm on one of said crank pins containing aplane of movementintervening between the planes of movement of adjacentarms on the opposite pin, and means for rotating the shaft.

15. For debarking a piece of wood, a machine comprising a carrier fortransporting a piece of wood along a predetermined path, a rotor havingits axis of rotation extending transversely of the path at one sidethereof, and hammers pivotally mounted on the periphery of the rotor toswing a planar paths perpendicular to said axis and to project radiallytherefrom in response to centrifugal force, the distance between saidpredetermined path and axis being such that the hammers strike suchpiece of wood glancing blows as it is transported past the rotor by thecarrier, the rotor comprising a series of plates disposed transverselyof the axis, each plate being elongate transversely of the rotor axisand having an opening near eachend, the longer dimensions of alternateplates being at right angles to each other, shafts extendingthrough theopenings at corresponding ends of the several plates, the

hammers being pivotally mounted on said shafts and located in'the spacesbetween alternate plates, each hammer having a curved impact element atthe leading side of its outer end.

16. Apparatus for debarking pieces of wood comprise 7 port pieces ofwood past the rotor along a path close enough to the rotor so thatsubstantially all the hammers can reach a piece irrespective of thecontour thereof, said recesses being disposed between planesperpendicular to the axis of the rotor with at least one recess betweeneach pair of adjacent planes, the width of the recesses beingsubstantially equal to the distance between planes and the width of thehammers being substantially equal to that of the recesses, so that thehammers strike the pieces throughout substantially the enire lengh ofthe rotor and the pivoted end of each hammer may be as wide as itsprojecting portion.

References Cited in the file of this patent UNITED STATES PATENTSHansson Dec. 9, 1902 De Cew July 17, 1917 Cote Aug. 18, 1925 Noyes Sept.8, 1925 Hummel May 22, 1928 Pangborn June 12, 1928 Genes et a1. Oct. 11,1932 10 Council Mar. 13, 1934 Kenney Apr. 2, 1946 Daniell Feb. 24, 1948Williford June 10, 1952 Eklund et a1 Aug. 26, 1952 Kolpe et a1 July 21,1953 Denison Sept. 29, 1953 FOREIGN PATENTS Sweden Dec. 5, 1896 SwedenOct. 16, 1918 France Jan. 7, 1944 Great Britain Oct. 31, 1951

